(I'm not the anon who posted the site)
Sites like that usually don't own or claim copyright. If they charge a fee, it's usually as compensation for the effort of making a hi-res scan and cleaning it up, if you're a company and making commercial prints, you'd want a higher quality file so your stuff doesn't look like dinky homemade printables, so if someone has taken the trouble to do a nice, clean, high-res scan, it's worth the $20 to not have to re-scan and clean it up yourself. You're not paying for copyright at all, just a better scan.
Anytime someone says it's a "vintage" graphic, the assumption is that it's so old it has passed out of copyright and into public use. Copyright doesn't last forever, it expires after a few decades. The whole concept was argued out the last time someone said Meta used some other graphic, which is why nobody's bothering to explain it in this thread. So no, this isn't copyright violation. IW didn't draw the rabbit, but IW rarely ever does their own art. IW and JetJ both like to go the vintage art route, using free-use graphics on their dresses, which is why JetJ can use stuff like famous old paintings, this isn't something new either, which is also why nobody is batting any eyes at this "copyright" issue except the angry newbies. It's a common comment for JetJ because their dresses are $$$$ despite using free graphics.
I'll rehash the part about characters as well -- characters like Mickey Mouse are also subject to this, which is why Disney likes to make shitty sequels. Every time they make a sequel they kind of re-copyright the character, so every sequel means the character stays copyrighted as theirs, which is why Mickey Mouse still isn't free for you to use despite Walt Disney himself being dead for awhile. Random rabbits don't have this going on, which again is why anons are saying "it's just bunnies", as it's unlikely to be something someone made sequels of to renew the copyright on.
Much clearer now, I hope.